Configuration resistors are used by configuration circuits to determine digital codes. These digital codes are often used to configure parameters of integrated circuits (ICs) such as I2C bus addresses, boot options, device vendor information (e.g. part family or capacity), and other parameters. The number of unique digital codes that can be represented by a single resistor under test is limited by the resolution and accuracy with which a configuration circuit of the IC can determine resistance. Often the resistance is determined by measuring a value that is proportional to resistance, such as by measuring a voltage at a terminal of the resistor.
Some attempted solutions use a fixed current source to develop a fixed test voltage at a terminal of a configuration resistor and compare that fixed test voltage to a varying reference voltage. The result of the comparison is used to obtain a digital code.
Some attempted solutions use a varying current mirror circuit to develop both a varying test voltage at a terminal of a configuration resistor and a varying reference voltage. The varying test voltage is compared to the varying reference voltage. The result of the comparison is used to obtain a digital code. Because a current mirror circuit is used to develop the test voltage and the reference voltage, the test voltage and the reference voltage vary dependently.
Some attempted solutions use an analog-to-digital converter (ADC) coupled to a terminal of a configuration resistor. The ADC creates a digital representation of an analog signal at a terminal of a configuration resistor. The digital representation is used to obtain a digital code.